Initiation and propagation of calcium-dependent action potentials in a coupled network of olfactory interneurons

Coherent oscillatory electrical activity and apical-basal wave propagation have been described previously in the procerebral (PC) lobe, an olfactory center of the terrestrial slug Limax maximus. In this study, we investigate the physiological basis of oscillatory activity and wave propagation in the PC lobe. Calcium green dextran was locally deposited in the PC lobe; this led to cellular uptake and transport of dye by bursting and nonbursting neurons of the PC lobe. The change of intracellular calcium concentration was measured at several different positions in neurites of individual bursting neurons in the PC lobe with a two-photon laser-scanning microscope. Fluorescence measurements were also made from neurons intracellularly injected with calcium green-1. Two different morphological classes of bursting neurons were found, varicose (VB) and smooth (SB). Our results from concurrent optical and intracellular recordings suggest that Ca2+ is the major carrier for the inward current during action potentials ...